Structure and method for gated lateral bipolar transistors

ABSTRACT

An improved structure and method for gated lateral bipolar transistors is provided. The present invention capitalizes on opposing sidewall structures and adjacent conductive sidewall members to conserve available surface space on the semiconductor chips. The conserved surface space allows a higher density of structures per chip. The conductive sidewall members couple to the gate of the gated lateral bipolar transistor and, additionally, to a retrograded, more highly doped bottom layer. The improved structure provides for both metal-oxide semiconductor (MOS) type conduction and bipolar junction transistor (BJT) type conduction beneath the gate of the gated lateral bipolar transistor.

RELATED APPLICATIONS

1. This application is related to the following co-filed and commonlyassigned applications; attorney docket number 303.413us1, entitled“Circuit and Method for Low Voltage, Voltage Sense Amplifier,” attorneydocket number 303.402us1, entitled “Circuit and Method for Low Voltage,Current Sense Amplifier,” and attorney docket number 303.471us1,entitled “Circuit and Method for Gate-Body Structures in CMOSTechnology,” which are hereby incorporated by reference.

FIELD OF THE INVENTION

2. The present invention relates generally to semiconductor integratedcircuits. More particularly, it pertains to the structure andfabrication of gated lateral bipolar transistors.

BACKGROUND OF THE INVENTION

3. Integrated circuit technology relies on transistors to formulate vastarrays of functional circuits. The complexity of these circuits requirethe use of an ever increasing number of linked transistors. As thenumber of transistors required increases, the surface area on a siliconchip/die that can be dedicated to a single transistor dwindles. It isdesirable then, to construct transistors which occupy less surface areaon the silicon chip/die.

4. Integrated circuits are predominantly designed with one of two typesof transistors. These two types are metal-oxide semiconductor (MOS)transistors and bipolar junction transistors (BJTs). MOS transistors areprevalent in integrated circuit technology because they generally demandless power than their counterpart, bipolar transistors. Bipolartransistors, on the other hand, also possess certain advantages over MOStransistors, such as speed. Therefore, attempts have been made tocombine the technological designs of bipolar transistors and MOStransistors in an effort to maximize the benefits of both transistortypes.

5. Various types of lateral MOS transistors have been historicallydescribed and utilized in complementary metal oxide semiconductor (CMOS)technology. Lateral bipolar transistors have received renewed interestwith the advent of bipolar complementary metal oxide semiconductor(BiCMOS) technologies. Recently newer devices have been developed whichhave both MOS and bipolar characteristics and functionality. A morecareful distinction is made between the different types of transistoraction possible in the newer devices. These newer devices include theso-called “gate-body” connected MOS transistor and the “gated lateral”bipolar transistor. The term gate-body connected transistors is used todescribe vertical or other device structures where the body of the MOStransistor also serves as the base of a bipolar transistor but eachdevice functions separately as a normal transistor and MOS transistoraction is dominant. A voltage applied to the gate region of thestructure is also directly input into the body of the semiconductormaterial. This results in reducing the threshold voltage of the MOStransistor.

6. In a gated lateral transistor, not only the structures but also theoperation is merged and most current flows along the surface under thegate in either MOS or bipolar operation. At low gate voltages aroundthreshold (V_(t)), the gated lateral bipolar transistors can act asgate-body connected MOS transistors. At higher input voltages, V_(t) ormore, the bipolar action can dominate and they are more appropriatelydescribed as gated lateral bipolar transistors.

7. One problem with conventional designs of gate-body and gated lateraltransistors is that they use up precious die space in the fabrication ofintegrated circuits. What is needed is a structure which can offermerged transistor action, yet also conserve space on the chip's surface.Structures which conserve space contribute toward higher densityfabrication, and increased utility for integrated circuits. It isdesirable that any improved configuration for transistor structure beadaptable to present integrated circuit design. Thus, it is an objectiveto uncover newly configured transistors which conserve chip space andwhich can be employed in conventional digital circuit technology.

SUMMARY OF THE INVENTION

8. In one embodiment, a gated lateral bipolar transistor is provided.The gated lateral bipolar transistor is a single crystallinesemiconductor structure. The structure has an upper surface and opposingsidewall surfaces. The single crystalline semiconductor structure has aretrograded and more highly doped bottom layer/well. There is asource/emitter region and a collector/drain region on the upper surface.A dielectric layer is formed on the upper surface as well as on theopposing lower sidewall surfaces of the single crystalline semiconductorstructure. A gate is located above the dielectric layer, above the uppersurface of the single crystalline semiconductor structure. Conductivesidewall members are included which couples to the gate. This sidewallmember additionally couples to the opposing sidewall surfaces. The gatedlateral bipolar transistor gives both BJT and MOS action.

9. In another embodiment, a gated lateral bipolar transistor is formedon a semiconductor substrate. The transistor has a first layer ofsemiconductor material extending outwardly from the substrate. The firstlayer of semiconductor material includes an upper surface and hasopposing sidewall surfaces. There is a second layer of semiconductormaterial formed on and extending outwardly from the upper surface of thefirst layer of semiconductor material. Like the first layer ofsemiconductor material, the second layer of semiconductor material hasopposing sidewall surfaces and an upper surface. On its upper surface,the second layer of semiconductor material has a source/emitter regionand a collector/drain region. A dielectric layer is formed over theupper surface of the second layer of semiconductor material and alsoover the opposing sidewall surfaces of both the first and second layersof semiconductor material. A gate is formed on this dielectric layer.And, a conductive sidewall member is disposed adjacent to portions ofthe dielectric layer. The conductive sidewall member also couples toportions of the first layer of semiconductor materials.

10. In another embodiment, the gated lateral bipolar transistor isformed on an insulator layer formed on a p+ silicon material substrate.A first layer of semiconductor material extends outwardly from theinsulator layer and has opposing sidewall surfaces and an upper surface.A second layer of semiconductor material extends outwardly from theupper surface of the first layer of semiconductor material along withopposing sidewall surfaces. An upper surface of the second layer ofsemiconductor material is provided with a source/emitter region and acollector/drain region. A dielectric layer formed on the upper surfaceof this second layer of semiconductor material, and likewise on theopposing sidewall surfaces of both the first and second layers ofsemiconductor material. There is again a gate formed on the dielectriclayer. Conductive sidewall members are disposed adjacent to the opposingsidewall surfaces. The conductive sidewall members additionally coupleto the gate. The conductive sidewall members have electrical contact toportions of the first layer of semiconductor material. In thisembodiment, the insulator layer is formed of an oxide layer, and thefirst layer of semiconductor material is more highly doped than thesecond layer of semiconductor material. The conductive sidewall membersare formed of polysilicon. This gated lateral bipolar transistor givesboth BJT and MOS action beneath the gate and is adapted to operate at avoltage input no greater than 1.5 volts.

11. The present invention also provides a method of fabrication for agated lateral bipolar transistor. In one embodiment, the method offabrication includes forming a planar body that extends outwardly from asemiconductor substrate. The planar body is formed to include a topsurface and a pair of sidewalls. A dielectric layer is formed on the topsurface as well as on the pair of sidewalls. A gate is then formed onthe dielectric layer. Forming the gate includes disposing the gateadjacent to the top surface and to the pair of sidewalls of the planarbody. A source/emitter region is implanted into the top surface of theplanar body. A drain/collector region is also implanted into the topsurface. The method of fabricating the gated lateral bipolar transistorincludes providing for both bipolar junction transistor (BJT) andmetal-oxide semiconductor (MOS) type conduction in the planar body. Themethod includes forming the planar body to have a retrograded well ofhighly doped silicon material. The method of fabrication furtherincludes adapting the gated lateral transistor to operate with voltageinput if no greater than 1.5 volts.

12. Another method of fabricating a gated lateral bipolar transistorincludes forming a first layer of semiconductor material that extendsoutwardly from a semiconductor substrate. A second layer ofsemiconductor material is formed on the first layer of semiconductormaterial. The second layer of semiconductor material is formed toinclude a source/emitter region and a collector/drain region. The methodincludes forming an first insulator layer on the second layer ofsemiconductor material and forming a second insulator layer underneaththe first layer of semiconductor material. A gate is formed on thesecond insulator layer and around portions of the first and secondlayers of semiconductor material. The gate is formed to couple toportions of the first layer of semiconductor material. This methodincludes forming the first and second layers of semiconductor materialof differently doped silicon material.

13. Another embodiment for fabricating a gated lateral bipolartransistor includes forming a first body type to extend outwardly from asemiconductor substrate. The first body type is formed with a topsurface and opposing sidewall surfaces. The method includes forming asecond body type on top of the first body type. The second body type issimilarly formed to have a top surface and opposing sidewall surfaces.The second body type is also formed with a source/emitter region and acollector/drain region. In this method, a first insulator layer isformed on the upper surface of the second body type and on portions ofthe opposing sidewall surfaces of the first and second body types. Asecond insulator layer is formed between the first body type and thesemiconductor substrate. The method further includes forming a gate overthe first insulator layer above the top surface of the second body type.Conductive sidewall members are formed and coupled to the gate. Themethod also includes coupling the conductive sidewall members to thefirst layer of semiconductor material.

14. Thus, an improved structure and method for fabricating gated lateralbipolar transistors is provided. The present invention capitalizes onopposing sidewall structures and adjacent conductive sidewall members toconserve available surface space on the semiconductor chips.Conservation of surface space achieves a higher density of surfacestructures per chip.

15. These and other embodiments, aspects, advantages, and features ofthe present invention will be set forth in part in the description whichfollows, and in part will become apparent to those skilled in the art byreference to the following description of the invention and referenceddrawings or by practice of the invention. The aspects, advantages, andfeatures of the invention are realized and attained by means of theinstrumentalities, procedures, and combinations particularly pointed outin the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

16.FIG. 1A is a perspective view of an embodiment of the gated lateralbipolar transistor according to the teachings of the present invention.

17.FIG. 1B is a top view of an embodiment of the gated lateral bipolartransistor shown in FIG. 1A.

18.FIG. 1C is an end view of an embodiment of the gated lateral bipolartransistor shown in FIG. 1A.

19.FIGS. 2A-2K illustrate an embodiment of the various processing stepsfor fabricating a complementary pair of gated lateral bipolartransistors.

DETAILED DESCRIPTION

20. In the following detailed description of the invention, reference ismade to the accompanying drawings which form a part hereof, and in whichis shown, by way of illustration, specific embodiments in which theinvention may be practiced. These embodiments are described insufficient detail to enable those skilled in the art to practice theinvention. Other embodiments may be utilized and structural, logical,and electrical changes may be made without departing from the scope ofthe present invention. The terms wafer and substrate used in thefollowing description include any structure having an exposed surfacewith which to form an integrated circuit (IC) structure using theinvention. The term substrate is understood to include semiconductorwafers. The term substrate is also used to refer to semiconductorstructures during processing, and may include other layers that havebeen fabricated thereupon. Both wafer and substrate include doped andundoped semiconductors, epitaxial semiconductor layers supported by abase semiconductor or insulator, as well as other semiconductorstructures well known to one skilled in the art. The term conductor isunderstood to include semiconductors, and the term insulator is definedto include any material that is less electrically conductive than thematerials referred to as conductors. The following detailed descriptionis, therefore, not to be taken in a limiting sense, and the scope of thepresent invention is defined only by the appended claims, along with thefull scope of equivalents to which such claims are entitled.

Structure

21.FIG. 1A is a perspective view illustrating one embodiment of a gatedlateral bipolar transistor 50, according to the teachings of the presentinvention. FIG. 1A illustrates that the gated lateral bipolar transistor50 has a single crystalline semiconductor structure 60. The singlecrystalline semiconductor structure 60 has an upper surface 70, opposingsidewall surfaces 80, and a bottom layer 190. The single crystallinesemiconductor structure 60 has a source/emitter region 100 and acollector/drain region 105 on the upper surface 70. A dielectric layer120 is formed on the upper surface 70 and the opposing sidewall surfaces80 of the single crystalline semiconductor structure 60. A gate 130 isformed on the dielectric layer 120. Conductive sidewall members 140couple to the gate 130. The conductive sidewall members further coupleto the opposing sidewall surfaces 80 on the bottom layer 190 viaconductive contacts 170. The bottom layer 190 forms a retrograded, morehighly doped, well or bottom layer to the single crystallinesemiconductor structure 60. In one embodiment, the retrograded bottomlayer 190 of the single crystalline semiconductor structure 60 is formedof p+ silicon material. In an alternative embodiment, the retrogradedbottom layer 190 of the single crystalline semiconductor structure 60 isformed of n+ silicon material. The gated lateral bipolar transistor 50is formed on an insulator layer 160 which is itself formed on a p+silicon substrate 180.

22.FIG. 1B provides a top view of the structure shown in FIG. 1A. TheFIG. 1B illustrates the source/emitter region 100 and thecollector/drain region 105. FIG. 1B also illustrates the gate 130resting on the dielectric layer 120. Also shown in FIG. 1B are theconductive sidewall members 140 which couple to the opposing sidewallsurfaces 80 of the single crystalline semiconductor structure 60.

23.FIG. 1C provides an end view of the structure shown in FIG. 1A.Included in FIG. 1C is the retrograded bottom layer 190 of the singlecrystalline semiconductor structure 60. The end view of FIG. 1Csimilarly illustrates the gate region 130 formed on the dielectric layer120. FIG. 1C illustrates the conductive sidewall members 140 coupling tothe opposing sidewall surfaces 80 at the bottom layer region 190 of thesingle crystalline silicon semiconductor structure 60 via conductivecontacts 170. In one embodiment, the gate 130 and the conductivesidewall members 140 are independently formed materials. In analternative embodiment, the gate 130 and the conductive sidewall members140 are one continuous structure.

24. In another embodiment, also exemplified by FIG. 1A, the singlecrystalline semiconductor structure 60 of the gated lateral bipolartransistor 50 includes a first layer of semiconductor material 190 and asecond layer of semiconductor material 200. The first layer ofsemiconductor material 190 extends outwardly from an insulator layer160. The first layer of semiconductor material 190 has opposing sidewallsurfaces 80 and an upper surface 210. The second layer of semiconductormaterial 200 extends outwardly from the upper surface 210 of the firstlayer of semiconductor material 190. The second layer of semiconductormaterial 200 also includes opposing sidewall surfaces 80 and has anupper surface 220. The second layer of semiconductor material 200includes a source/emitter region 100 and a collector/drain region 105. Adielectric layer 120 is formed on the upper surface of the second layerof semiconductor material 200, as well as on the opposing sidewallsurfaces 80 of the first and second layers of semiconductor material,190 and 200 respectively. A gate 130 is formed on the dielectric layer120. Conductive sidewall members are disposed adjacent to portions ofthe dielectric layer 120 on the opposing sidewall surfaces 80 of thefirst and second layers of semiconductor material, 190 and 200respectively. The conductive members 140 couple to portions of the firstlayer of semiconductor material 190 via conductive contacts 170.

25. In one embodiment, the first layer of semiconductor material 190 ofthe gated lateral bipolar transistor 50 is a first conductivity type andthe second layer of semiconductor material 200 is of the sameconductivity type. The substrate is formed of p+ silicon material. Thefirst layer of semiconductor material 190 is a p+ silicon material. Inan alternative embodiment, the first layer of semiconductor material isan n+ silicon material. The conductive sidewall members have conductivecontacts 170 to the first layer of semiconductor material 190.

Operation

26. The operation of the gated lateral bipolar transistor 50 is given byapplying a potential to the gate 130. Applying potential to the gate 130creates an inversion region in the second layer of semiconductormaterial 200 of the single crystalline semiconductor structure 60. Theinversion region allows conduction between the source/emitter region 100and the collector/drain region 105. The conduction occurs along theupper surface 220 of the second layer of semiconductor material 200. Atlow values of applied potential close to the threshold potential (V_(t))the gated lateral bipolar transistor 50 exhibits metal oxidesemiconductor (MOS) conduction action. In the exemplary embodiment, thegated lateral bipolar transistor operates at a voltage input of nogreater than 1.5 volts. For greater applied potentials larger thanV_(t), the gated lateral bipolar transistor 50 exhibits bipolar junctiontransistor (BJT) conduction action in addition to the MOS conductionaction. For even higher applied potentials much greater than V_(t), theBJT conduction action dominates. At the higher applied potential levels,the bipolar junction transistor conduction action results from theapplied potential being injected directly into the first layer ofsemiconductor material 190. In both the BJT and MOS conduction modes,the conduction occurs in the upper surface 220 of the second layer ofsemiconductor material 200 beneath the gate 130.

Method of Fabrication

27.FIGS. 2A through 2K illustrate an embodiment of the variousprocessing steps for fabricating a complementary pair of gated lateralbipolar transistors. FIG. 2A begins with a p+ doped silicon substrate300. A p− layer 310 is grown directly on the p+ layer 300. The p− layer310 is epitaxially grown to a thickness of approximately 0.5 micrometers(μm). Next, a nitride layer 320, formed of silicon nitride (Si₃N₄), isdeposited on the p− layer 310. The nitride layer 320 can be depositedthrough any suitable process, such as chemical vapor deposition (CVD). Aphoto resist is applied and selectively exposed to provide a mask todefine a p-channel metal oxide semiconductor (PMOS) device region 321.The nitride layer 320 is etched through a process such as reactive ionetching (RIE) to expose the silicon material underneath.

28.FIG. 2B illustrates the structure after the next series of steps. Thep− silicon layer 310 and the p+ silicon layer 300 are etched to a depthof approximately 0.7 μm to form a trench 325. An oxide layer 319 isformed and directionally etched to leave on the vertical sidewalls ofthe trench 325 created by the previous etching step. In one embodiment,the oxide layer 319 is grown, such as through thermal oxidation. In analternative embodiment, the oxide is deposited through any suitableprocess, such as chemical vapor deposition (CVD). The oxide layer 319 isetched through the process of reactive ion etching (RIE). An n+ layer330 is formed within the trench 325. In one embodiment, the n+ layer 330is grown to a thickness of approximately 0.2 μm through the process ofepitaxial growth. In an alternative embodiment, the n+ layer 330 isbegun with intrinsic epitaxial growth, followed by ion implantation ofthe n+ silicon material. Next, an n− layer 340 is formed on the surfaceof the n+ layer 330. The n− layer 340 is grown to a thickness ofapproximately 0.5 μm, sufficient to fill trench 325 to the same level asthe original upper surface 345 of the p− silicon layer 310. The nitridelayer 320 is stripped and the upper surface 345 is planarized throughany suitable process. In one embodiment, the upper surface 345 isplanarized through the process of chemical mechanicalpolishing/planarization (CMP). The structure is now as shown in FIG. 2B.

29.FIG. 2C represents the structure following the next sequence ofprocessing steps. An oxide layer 350 is formed on and across the uppersurface 345 of the p− layer 310 and the n− layer 340. A p+ polysilicongate material 360A is deposited across the surface of the oxide layer350. The p+ layer 360A is formed to a thickness of approximately 0.2 μm.The p+ gate material 360A can be deposited through any suitable method,such as through chemical vapor deposition (CVD). A photoresist isapplied and selectively exposed to provide a mask-defining an n-channelmetal oxide semiconductor (NMOS) device region 322. An n+ gate material360B is formed in the NMOS device region 322 through a process such asion implantation of n-type impurity ions. The structure is now asappears in FIG. 2C.

30.FIG. 2D illustrates the structure after the next sequence ofprocessing steps. The photoresist has been stripped, using conventionalphotoresist stripping techniques. A nitride pad 370 is formed on andacross the surface of the n+ gate material 360B and the p+ gate material360A. The nitride pad 370 is deposited by any suitable process, such aschemical vapor deposition (CVD). The nitride pad is deposited to athickness of approximately 0.4 μm. A photoresist is applied andselectively exposed to provide a mask which defines and covers the PMOSand NMOS device regions, 321 and 322 respectively. The nitride cap 370in between device regions, 321 and 322, is removed. The nitride cap 370is removed by any suitable etching technique, such as by RIE. The p+gate material 360A in between device regions, 321 and 322, is removed.And, the gate oxide 350 in between device regions, 321 and 322, isremoved. Each of these materials can be removed by etching using the RIEtechnique.

31. Still using the photoresist as a mask, the etching process iscontinued into the p− layer 310 and the p+ layer 300 of the silicon to adepth of approximately 0.2 μm below the bottom of the n+ layer 330. Theetching is performed through any suitable process, such as by RIE. Theseetching steps leave trenches 342 between the device regions 321 and 322.The structure is now as shown in FIG. 2D. The photoresist is nextstripped, using conventional photoresist stripping techniques.

32.FIG. 2E illustrates the structure after the next series of processingsteps. An insulator layer 380 is formed beneath the device regions, 321and 322 respectively. The insulator layer 380 is formed using silicon oninsulator (SOI) processing techniques. One skilled in the art willrecognize that there exist various approaches to forming an insulatorlayer underneath active device regions. The insulator layer 380 isformed using, for example, the techniques of U.S. application Ser. No.08/745,708, entitled Silicon-On-Insulator Islands and Method for TheirFormation (the '708 application), or U.S. Pat. No. 5,691,230, entitledTechnique for Producing Small Islands of Silicon on Insulator (the '230patent). The '708 application and the '230 patent are incorporated byreference.

33. Another method or approach is known as silicon insulated metal-oxide(SIMOX). This method creates a blanket buried oxide layer within thestarting substrate. Any suitable technique may be used, and since such aprocess is not part of the present invention, these steps are notrecited. Intrinsic polysilicon 390 is deposited by any suitable methods,such as by CVD, to fill the trenches 342. Next, the trenches 342 areplanarized stopping on the nitride pads 370. The intrinsic polysilicon390 in trenches 342 can be planarized by any suitable process, such asby chemical mechanical polishing/planarization (CMP). The intrinsicpolysilicon is directionally etched back to leave approximately 0.1-0.2μm at the bottom of the trenches 342. The etch can be performed usingany suitable method such as reactive ion etching (RIE). Oxide spacer 400is deposited such as by CVD to fill trenches 342. The oxide spacer 400is etched back to approximately 0.4 μm to the level of the top of thegates, 360A or 360B. A nitride spacer 403 is deposited such as by CVD.The nitride spacer 403 is directionally etched to leave on the exposedvertical sidewalls of the nitride pads 370. The structure is now asshown in FIG. 2E.

34.FIG. 2F illustrates the structure following the next sequence ofprocess steps. The oxide 400 and intrinsic polysilicon 390 aredirectionally etched using the nitride spacer 403 overhang as a mask. Ann+ polysilicon layer 410A is deposited by CVD. The n+ polysilicon 410Ais etched, such as by reactive ion etching, to leave on the verticalsidewalls of the oxide spacer 400. The n+ polysilicon layer 410A servesas the conductive sidewall members for the PMOS device region 321. Thestructure is now as shown in FIG. 2F

35.FIG. 2G illustrates the structure after the next sequence of processsteps. Silicon dioxide 405 is deposited in the trenches 342 and thenplanarized using CMP. The silicon dioxide 405 may be deposited by anysuitable method, such as by CVD. A photoresist is applied andselectively exposed to reveal only the NMOS device regions 322. Theexposed n+ polysilicon 410A is selectively etched to remove from thesidewalls of the NMOS device regions 322. A p+ polysilicon layer 410B isthen deposited by CVD to fill the slots left from removal of the n+polysilicon 410A and is then removed from the top surface by anysuitable method, such as RIE or CMP. The p+ polysilicon layer 410Bserves as the conductive sidewall members for the NMOS device region322. The structure is now as shown in FIG. 2G.

36.FIG. 2H illustrates the structure following the next sequence ofprocess steps. A phosphoric acid is applied to remove the nitride cap370 and the nitride spacer 403 from the active device regions, 321 and322 respectively. Removal of the nitride cap 370 and the nitride spacer403 exposes the p+ and n+ gate material, 360A and 360B respectively. Agate contact 420 is deposited, such as by CVD, over the p+ and n+ gateregions, 360A and 360B respectively. In one embodiment, the gate contact420 is formed of tungsten (W). In another embodiment, the gate contact420 is any other suitable refractory metal. The gate contact 420 isplanarized, such as by CMP, such that the gate contact 420 is left onlyover the p+ and n+ gate regions, 360A and 360B respectively. The deviceis now as shown in FIG. 2H.

37.FIG. 2I is a cross sectional view along cut line 2I—2I of FIG. 2H.FIG. 2I illustrates the structure after the following sequence ofprocess steps. A photoresist is applied and selectively exposed to maskthe gate regions 344. The exposed gate contact 420 and the n+ or p+polysilicon gate material, 360B and 360A, are etched to the underlyinggate oxide 350. The etching may be performed using RIE.

38.FIG. 2J is a top view of FIG. 2I. Using the same mask, the p+ or n+polysilicon layers 410B and 410A, located between the device regions 321and 322, are removed by etching. The etching can be performed using anysuitable method, such as RIE.

39.FIG. 2K illustrates the structure following the final series ofprocess steps. The photoresist is removed using conventional photoresiststripping techniques. An anneal is performed to out diffuse boron fromthe p+ layer 305 and to out diffuse phosphorous (or arsenic) from n+layer 330. The anneal also serves to out diffuse these same dopants fromthe p+ and n+ polysilicon layers, 410B and 410A respectively. Hence, theannealing serves to dope the adjoining sandwiched intrinsic polysilicon390. Boron and phosphorus (or arsenic), respectively, will out diffuseinto the intrinsic polysilicon 390 in approximately equal amounts. Thisprocess step effectively enhances the thickness of the p+ and n+polysilicon conductive sidewall members, 410B and 410A respectively.

40. A photoresist is applied and exposed to cover the NMOS gated lateralbipolar transistor 51. Then, a p+ source/emitter region 450A and acollector/drain region 451A are ion implanted using self-aligningprocess techniques with the gate 360A. The photoresist is then strippedusing conventional photoresist stripping techniques.

41. Another photoresist is applied and exposed, this time to cover thePMOS gated lateral bipolar transistor 52. Another ion implantation stepis used to form an n+ source/emitter region 450B and a collector/drainregion 451B in the NMOS gated lateral bipolar transistor 52. Thephotoresist is once again removed. The structure is now as shown in FIG.2K.

42. Contact holes and wiring are achieved through conventionalprocessing steps. One skilled in the art will recognize the method tothese steps and, hence, they are not disclosed as part of thisapplication.

Conclusion

43. An improved structure and method for fabricating gated lateralbipolar transistors is provided. The present invention capitalizes onopposing sidewalls and adjacent conductive sidewall members to conserveavailable surface space on the semiconductor chips. Conservation ofsurface space achieves a higher density of surface structures per chip.

44. It is to be understood that the above description is intended to beillustrative, and not restrictive. Combinations of the aboveembodiments, and other embodiments will be apparent to those of skill inthe art upon reviewing the above description. The above structures andfabrication methods have been described, by way of example, not by wayof limitation, with respect to the transistors, gain memory cell, memorycell array and memory device. However, the scope of the inventionincludes any other integrated circuit applications in which the abovestructures and fabrication methods are used. Thus, the scope of theinvention is not limited to the particular embodiments illustrated anddescribed herein. The scope of the invention should be determined withreference to the appended claims, along with the full scope ofequivalents to which such claims are entitled.

What is claimed is:
 1. A gated lateral bipolar transistor, comprising: asingle crystalline semiconductor structure having an upper surface,opposing sidewall surfaces and a bottom layer, the single crystallinesemiconductor structure having a source/emitter region and having acollector/drain region on the upper surface; a dielectric layer formedon the upper surface and on portions of the opposing sidewall surfacesof the single crystalline semiconductor structure; and a gate formed onthe dielectric layer above the upper surface and around portions of theopposing sidewall surfaces, the gate coupling to the bottom layer of thesingle crystalline semiconductor structure, such that the transistorexhibits both bipolar junction transistors (BJT) and metal-oxidesemiconductor (MOS) action.
 2. The gated lateral bipolar transistor ofclaim 1 , wherein the bottom layer is retrograded and more highly dopedthan the remainder of the single crystalline semiconductor structure. 3.The gated lateral bipolar transistor of claim 1 , wherein the singlecrystalline semiconductor structure has a bottom layer of p+ siliconmaterial.
 4. The gated lateral bipolar transistor of claim 1 , whereinthe single crystalline semiconductor structure has a bottom layer of n+silicon material.
 5. The gated lateral bipolar transistor of claim 1 ,wherein the bottom layer of the single crystalline semiconductorstructure is formed on an insulator layer formed on a p+ siliconsubstrate.
 6. A gated lateral bipolar transistor, comprising: asemiconductor substrate; a first layer of semiconductor materialextending outwardly from a substrate; the first layer of semiconductormaterial having opposing sidewall surfaces and an upper surface; asecond layer of semiconductor material formed on and extending outwardlyfrom the upper surface of the first layer of semiconductor material, thesecond layer of semiconductor material having opposing sidewall surfacesand an upper surface, and the second layer of semiconductor materialhaving a source/emitter region and collector/drain region; a dielectriclayer formed on the upper surface of the second layer of semiconductormaterial and on the opposing sidewall surfaces of the first and secondlayers of semiconductor material; a gate formed on the dielectric layer;and conductive sidewall members disposed adjacent to portions of thedielectric layer formed on the opposing sidewall surfaces of the firstand second layer of semiconductor materials, and the conductive sidewallmembers further coupling to portions of the first layer of semiconductormaterial.
 7. The gated lateral bipolar transistor of claim 6 , whereinthe first layer of semiconductor material is formed on an insulatorlayer formed on the semiconductor substrate.
 8. The gated lateralbipolar transistor of claim 6 , wherein the first layer of semiconductormaterial is a first conductivity type and wherein the second layer ofsemiconductor material is a second conductivity type.
 9. The gatedlateral bipolar transistor of claim 6 , wherein the semiconductorsubstrate comprises p+ silicon material.
 10. The gated lateral bipolartransistor of claim 6 , wherein the gate couples to the conductivesidewall members.
 11. The gated lateral bipolar transistor of claim 6 ,wherein conductive sidewall members make conductive contact to the firstlayer of semiconductor material.
 12. A gated lateral bipolar transistor,comprising: a p+ silicon material substrate; an insulator layer formedon the substrate; a first layer of semiconductor material extendingoutwardly from the insulator layer; the first layer of semiconductormaterial having opposing sidewall surfaces and an upper surface; asecond layer of semiconductor material formed on and extending outwardlyfrom the upper surface of the first layer of semiconductor material, thesecond layer of semiconductor material having opposing sidewall surfacesand an upper surface, and second layer of semiconductor material havinga source/emitter region and collector/drain region; a dielectric layerformed on the upper surface of the second layer of semiconductormaterial and on the opposing sidewall surfaces of the first and secondlayers of semiconductor material; a gate formed on the dielectric layer;and conductive sidewall members, the conductive sidewall memberscoupling to the gate, and the conductive sidewall members disposedadjacent to portions of the dielectric layer formed on the opposingsidewall surfaces of the first and second layers of semiconductormaterial, and the conductive sidewall members having electrical contactto portions of the first layer of semiconductor material, and theconductive sidewall members operate conjunctively with the gate suchthat the transistor exhibits both bipolar transistor action (BJT) andmetal-oxide semiconductor (MOS) transistor action.
 13. The gated lateralbipolar transistor of claim 12 , wherein the insulator layer formed onthe semiconductor substrate comprises an oxide layer.
 14. The gatedlateral bipolar transistor of claim 12 , wherein the first layer ofsemiconductor material is more highly doped than the second layer ofsemiconductor material.
 15. The gated lateral bipolar transistor ofclaim 12 , wherein conductive sidewall members are polysilicon.
 16. Thegated lateral bipolar transistor of claim 12 , wherein the electricalcontact of the conductive sidewall members to the first layer ofsemiconductor material gives bipolar junction transistor (BJT) actionbeneath the gate.
 17. A method of fabricating a gated lateral bipolartransistor, the method comprising: forming a planar body that extendsoutwardly from a semiconductor substrate, wherein the planar bodyincludes a top surface and a pair of sidewalls; forming an insulatorlayer on the top surface and on the pair of sidewalls of the planarbody; forming a gate outwardly from the insulator layer; implanting asource/emitter region into the top surface of the planar body; andimplanting a drain/collector region into the top surface of the planarbody such that the transistor provides both bipolar junction transistor(BJT) and metal-oxide semiconductor (MOS) action.
 18. The method offabricating a gated lateral bipolar transistor of claim 17 , whereinforming the planar body comprises forming a retrograded well of highlydoped silicon material.
 19. The method of fabricating a gated lateralbipolar transistor of claim 17 , wherein forming the gate comprisespolysilicon.
 20. The method of fabricating a gated lateral bipolartransistor of claim 17 , wherein forming the gate comprises forming afirst conductivity type material on the top surface of the planar bodyand forming a second conductivity type material on the pair of sidewallsof the planar body.
 21. The method of fabricating a gated lateralbipolar transistor of claim 17 , wherein forming the gate comprisescoupling the gate to the pair of sidewalls.
 22. A method of fabricatinga gated lateral bipolar transistor, the method comprising: forming afirst layer of semiconductor material that extends outwardly from asemiconductor substrate; forming a second layer of semiconductormaterial outwardly from the first layer of semiconductor material;forming a source/emitter region on the second layer; forming acollector/drain region on the second layer; forming a first insulatorlayer on the second layer of semiconductor material; and forming a gatethat extends over a portion of the first insulator layer above thesecond layer of semiconductor material, around portions of the first andsecond layers of semiconductor material, and that couples to portions ofthe first layer of semiconductor material.
 23. The method of fabricatinga gated lateral bipolar transistor of claim 22 , wherein the methodfurther comprises forming a second insulator layer underneath the firstlayer of semiconductor material.
 24. The method of fabricating a gatedlateral bipolar transistor of claim 22 , wherein forming the first andsecond layers of semiconductor material comprises forming oppositelydoped layers of silicon material.
 25. The method of fabricating a gatedlateral bipolar transistor of claim 22 , wherein forming the first layerof semiconductor material comprises forming a layer of semiconductormaterial with a higher doping concentration than the second layer ofsemiconductor material.
 26. A method of fabricating a gated lateralbipolar transistor, the method comprising: forming a first layer ofsemiconductor material that extends outwardly from a semiconductorsubstrate, wherein the first layer of semiconductor material includes atop surface and opposing sidewall surfaces; forming a second layer ofsemiconductor material on the first layer of semiconductor material,wherein the second layer of semiconductor material includes a topsurface and opposing sidewall surfaces; forming a source/emitter regionin the top surface of the second layer of semiconductor material;forming a collector/drain region in the top surface of the second layerof semiconductor material; forming a first insulator layer on the uppersurface of the second layer of semiconductor material and on portions ofthe opposing sidewall surfaces of the first and second layers ofsemiconductor materials; forming a gate over the first insulator layeron the top surface of the second layer of semiconductor material; andforming conductive sidewall members, wherein the conductive sidewallmembers couple to the gate, and wherein the conductive sidewall memberscouple to the first layer of semiconductor material.
 27. The method offabricating a gated lateral bipolar transistor of claim 26 , wherein themethod further comprises forming a second insulator layer sandwichedbetween the first layer of semiconductor material and the semiconductorsubstrate.
 28. The method of fabricating a gated lateral bipolartransistor of claim 26 , wherein forming the first and second layers ofsemiconductor material comprises forming oppositely doped layers ofsilicon material.
 29. The method of fabricating a gated lateral bipolartransistor of claim 26 , wherein forming the first layer ofsemiconductor material comprises forming a layer of semiconductormaterial with a higher doping concentration than the second layer ofsemiconductor material.